/* welcome 欢迎页 */
.mail {
    top: 5%;
    width: 100%;
    position: relative;
    text-align: center;
}

.mail > img {
    margin: 3% auto;
    display: block;
    position: relative;
    text-decoration: none;
    transition: 0.5s;
    opacity: 0;
    -webkit-animation: mail-btn 2s forwards 1.2s linear;
    -o-animation: mail-btn 2s forwards 1.2s linear;
    animation: mail-btn 2s forwards 1.2s linear;
}

@keyframes mail-btn {
    0% {
        opacity: 0;
        bottom: -600px;
    }
    50% {
        bottom: 0;
    }
    100% {
        opacity: 1;
        bottom: -30%;
    }
}